The view has been growing that eukaryotic genomes are "fluid" in the sense that mobile elements are frequently inserted and deleted. The study of the molecular biology of mobile DNA sequences will lead towards an understanding of the functional and evolutionary importance of the apparrently frequent events of DNA sequence rearrangement. We propose to examine the mobility of DNA sequences in eukaryotic species which exhibit typical genome organization including the interspersion of many short repeats throughout the single copy DNA. We propose to search for families of mobile elements in the human and sea urchin genomes and examine their primary sequences and characteristics as well as their relationship to interspersed repeated sequences. We propose to measure the number of families of mobile ssequences and the rates of transposition and thus estimate the global effects of mobility on the genomes. While current techniques will permit progress towards this goal we also propose to develop new techniques for rapid measurement of mobility. Sea urchin repeats contain short sequences with homology to viral enhancer sequences which appear to be statistically significant. As a part of this proposal we plan to test the function of these enhancer-like sequences using a sea urchin DNA transformation system recently developed in this laboratory. We propose to transform sea urchins with gene regions plus or minus inserts of the enhancer-like sequence and measure the effect on rates of transcription and timing of expression during development.